OFFSET
0,4
COMMENTS
It would be nice to have a formula or recurrence.
EXAMPLE
Row 4 of A294442 contains eight fractions,
1/5, 4/5, 3/7, 4/7, 2/7, 2/7, 3/8, 5/8.
There are three distinct denominators, so a(4) = 3.
MAPLE
# S[n] is the list of fractions, written as pairs [i, j], in row n of Kepler's triangle; nc is the number of distinct numerators, and dc the number of distinct denominators
S[0]:=[[1, 1]]; S[1]:=[[1, 2]];
nc:=[1, 1]; dc:=[1, 1];
for n from 2 to 18 do
S[n]:=[];
for k from 1 to nops(S[n-1]) do
t1:=S[n-1][k];
a:=[t1[1], t1[1]+t1[2]];
b:=[t1[2], t1[1]+t1[2]];
S[n]:=[op(S[n]), a, b];
od:
listn:={};
for k from 1 to nops(S[n]) do listn:={op(listn), S[n][k][1]}; od:
c:=nops(listn); nc:=[op(nc), c];
listd:={};
for k from 1 to nops(S[n]) do listd:={op(listd), S[n][k][2]}; od:
c:=nops(listd); dc:=[op(dc), c];
od:
nc; # A294443
dc; # A294444
CROSSREFS
KEYWORD
nonn,more
AUTHOR
N. J. A. Sloane, Nov 20 2017
STATUS
approved